"We have seen today the difference between a ship of peace activists...and a flotilla of hate that was organized by violent extremists," Netanyahu said.

The prime minister promised no retreat and no surrender from its three-year blockade.

"Israel will continue to exercise its rights to self-defense," Netanyahu said. "We will not allow the establishment of an Iranian port in Gaza."

Activists said they planned to send as many as three more ships in the coming months.

"What Israel needs to understand is that nothing is accomplished with force," said Greta Berlin of the Cyprus-based Free Gaza group, which sent the latest aid vessel, the Rachel Corrie.

The Rachel Corrie was carrying 19 people and hundreds of tons in aid when it was seized about 20 miles from the Gaza coast. Three small navy vessels approached the ship after it ignored orders to change course for Ashdod.

Israeli officials said they offered to deliver the aid to Gaza once it was thoroughly inspected.

As the Israelis were boarding the ship, angry demonstrators marched in Istanbul, London, Dublin and Paris to protest the blockade and last week's bloody shootout on the high seas.